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https://issues.apache.org/jira/browse/FLINK-7144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16457685#comment-16457685
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Rong Rong commented on FLINK-7144:
----------------------------------
FLINK-8689 has been merged and FLINK-8690 is on the way. Will fix this one as
well :-)
> Optimize multiple LogicalAggregate into one
> -------------------------------------------
>
> Key: FLINK-7144
> URL: https://issues.apache.org/jira/browse/FLINK-7144
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Jark Wu
> Assignee: Rong Rong
> Priority: Major
>
> When applying multiple GROUP BY, and no aggregates or expression in the first
> GROUP BY, and the second GROUP fields is a subset of first GROUP fields.
> Then the first GROUP BY can be removed.
> Such as the following SQL ,
> {code}
> SELECT a FROM (SELECT a,b,c FROM MyTable GROUP BY a, b, c) GROUP BY a
> {code}
> should be optimized into
> {code}
> DataStreamGroupAggregate(groupBy=[a], select=[a])
> DataStreamCalc(select=[a])
> DataStreamScan(table=[[_DataStreamTable_0]])
> {code}
> but get:
> {code}
> DataStreamGroupAggregate(groupBy=[a], select=[a])
> DataStreamCalc(select=[a])
> DataStreamGroupAggregate(groupBy=[a, b, c], select=[a, b, c])
> DataStreamScan(table=[[_DataStreamTable_0]])
> {code}
> I looked for the Calcite built-in rules, but can't find a match one. So maybe
> we should implement one , and maybe we should implement it in Calcite.
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